Event unfortanely don't work so good. When I press one button and sound is playing and then press other button, where song is shorter, both turn to sprite 0, not only that one which end but also that one which is still playing.

If I understand you right with: ". I'd place different buttons as different animations to that single object."

I've one sprite object with diffrent animation frames for all buttons like there: ge.tt/6vClebw/v/0

The .capx I posted works for me, when you click on button it changes the frame to 1 while sound is playing. Sprites frame changes to 0 when it is not playing a sound effect. You can have as many buttons/sounds as you need. Wasn't that the goal or did I miss something? :)

Edit: As always, don't bother running anything HTML5 related in Internet Explorer as it won't work as intended.